1. Field of the Invention
The present invention relates to fuel injection control of internal combustion engines, and particularly, to a control apparatus for a four stroke cylinder direct-injection internal combustion engine that injects fuel directly into a cylinder.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 10-231744 discloses a configuration for controlling a fuel-injection amount and a fuel-injection timing in a so-called cylinder direct-injection internal combustion engine that injects fuel directly into a cylinder. Specifically, in this configuration, stratified combustion is performed by injecting fuel during the compression stroke when the engine is operating in a specific operating range of, for example, medium/high load. When performing stratified combustion, a fuel injection is performed during the intake stroke prior to the injection in the compression stroke. Specifically, the injection is performed such that the fuel injected during the intake stroke is prevented from pre-igniting and that a total air-fuel ratio determined from the total amount of fuel injected in the compression stroke and the intake stroke is made close to a stoichiometric air-fuel ratio. In Japanese Unexamined Patent Application Publication No. 10-231744, the stratified combustion is performed by injecting fuel towards a cavity provided at the top surface of a piston reciprocating in the cylinder.
An internal combustion engine that can vary the engine compression ratio by changing the position of the top dead center of the piston is known. For example, when the known internal combustion engine is running at high load, the compression ratio is reduced to a low value so as to prevent abnormal combustion, such as knocking. In such a variable compression ratio internal combustion engine, supposing that the reduction in the compression ratio is delayed during a transient state in which the engine compression ratio is varied, the occurrence of knocking can be prevented during the transient state by performing the fuel-injection control discussed in Japanese Unexamined Patent Application Publication No. 10-231744.